Higher Ce Content Research Articles

Performance changes in the anammox process under the stress of rare-earth element Ce(III) and the evolution of microbial community and functional genes

The high Ce(III) content in ionic rare-earth tailings wastewater has hindered the application of anammox process in this field. Here, the effect of Ce(III) on the performance of anammox processes was investigated, and the evolution of microbial communities and functional genes was explored using metagenomic sequencing. The results showed that the reactor nitrogen removal rate decreased when the Ce(III) concentration reached 25 mg/L, although ammonia nitrogen removal (92.31%) and nitrogen removal efficiency (81.33%) remained at a high level; however, both showed a significant decreasing trend. The relative abundance of anammox bacteria increased continuously from P1–P5, reaching 48.81%, whereas the relative abundance of Candidatus jettenia reached 33.71% at P5, which surpassed that of Candidatus brocadia as the most abundant anammox bacteria, and further analysis of functional genes and metabolic pathways revealed that Candidatus brocadia was richer in biochemical metabolic genes, whereas Candidatus jettenia had richer efflux genes.

Synthesis of Stable Cerium Oxide Nanoparticles Coated with Phosphonic Acid-Based Functional Polymers.

Functional polymers, such as poly(ethylene glycol) (PEG), terminated with a single phosphonic acid, hereafter PEGik-Ph are often applied to coat metal oxide surfaces during post-synthesis steps but are not sufficient to stabilize sub-10 nm particles in protein-rich biofluids. The instability is attributed to the weak binding affinity of post-grafted phosphonic acid groups, resulting in a gradual detachment of the polymers from the surface. Here, we assess these polymers as coating agents using an alternative route, namely, the one-step wet-chemical synthesis, where PEGik-Ph is introduced with cerium precursors during the synthesis. Characterization of the coated cerium oxide nanoparticles (CNPs) indicates a core-shell structure, where the cores are 3 nm cerium oxide and the shell consists of functionalized PEG polymers in a brush configuration. Results show that CNPs coated with PEG1k-Ph and PEG2k-Ph are of potential interest for applications as nanomedicines due to their high Ce(III) content and increased colloidal stability in cell culture media. We further demonstrate that the CNPs in the presence of hydrogen peroxide show an additional absorbance band in the UV-vis spectrum, which is attributed to Ce-O22- peroxo-complexes and could be used in the evaluation of their catalytic activity for scavenging reactive oxygen species.

Boosting the Rhodamine B adsorption of bimetallic Ce/Zr UiO-66: Effect of valence states of cerium precursor

Two kinds of Ce-doped UiO-66 were synthesized by using CeCl3·7H2O and (NH4)2Ce(NO3)6 as cerium precursors, namely Ce(III)- and Ce(IV)-UiO-66. The effect of valence states of cerium precursors on adsorption performance towards Rhodamine B (RhB) was investigated for the first time. Ce atoms are in two valence states of +3 and + 4, where Ce3+ ions turn their surfaces negatively charged. The higher cerium content (24.8%) and ratio of Ce3+/Ce4+ ions (1.4:1) of Ce(IV)-UiO-66 made its surface more negatively charged, which is contributed to form stronger electrostatic interaction with cationic dyes. The adsorption amounts of RhB were 239.5 mg/g and 431.7 mg/g for Ce(III)- and Ce(IV)-UiO-66, which are 2.38 and 5.11 times higher than pristine UiO-66, respectively. The well-fit Langmuir model and pseudo-second-order model suggest a monolayer chemisorption process. The adsorption mechanism suggests that the electrostatic interaction and the complexation interaction between Ce3+ and RhB are dominant factors affecting RhB adsorption. Since Ce3+ severed as adsorption sites, the higher Ce content and stronger electrostatic interaction of Ce(IV)-UiO-66 together promoted its RhB adsorption than Ce(III)-UiO-66. The obtained results help to understand how the mixed-valences of incorporated metals affect the adsorption behaviors of bimetallic MOFs deeply.

Synchronous enhancement mechanism of magnetic property for dual-main-phase Ce magnets by grain boundary diffusion with Pr-Al alloy

The Pr80Al20 (at%) alloy was diffused into the dual-main-phase Ce magnets (Ce/TRE = 40 wt.%, TRE: total rare earth) with different diffusion time by grain boundary diffusion process (GBDP). The magnetic property and the microstructure of a series of magnets with different diffusion time were investigated. The coercivity gradually increased as the diffusion time increased, while the remanence remained basically constant. The improvement of coercivity originated from the synergistic contribution of modified grain boundaries with decoupling effect and Ce-rich main phase containing Pr with improved magnetocrystalline anisotropy. The percentage of the irreversible portion and the nucleation field of the reverse domain calculated from recoil loops curves further confirmed that the diffusion of Pr80Al20 alloy enhanced the coercivity. The enhanced anisotropy of the Ce-rich grains compensates for the decay of the remanence carried by the diffusion-induced increase in the nonmagnetic grain boundary phase, which ultimately results in the remanence remaining essentially constant. The above phenomena further broaden the room-temperature applications of dual-main-phase magnets with high Ce content without heavy rare-earth grain boundary diffusion.

Strategy for Co-Enhancement of Remanence-Coercivity of RE-Fe-B Sintered Magnets with High Ce-Content: Appropriate La Substitution.

The development of low-cost RE-Fe-B sintered magnets with large La/Ce content is of great significance for the balanced utilization of rare earth (RE) resources, but it is limited by reduced magnetic properties. In this work, the coercivity (Hcj ), remanence (Br ), maximum energy product [(BH)max ], and temperature stability are simultaneously enhanced for magnets with LaCe accounting for 40wt% of the total RE. The synergistic regulation of the REFe2 phase, Ce-valence, and grain boundaries (GBs) in RE-Fe-B sintered magnets is realized for the first time by introducing appropriate La elements. The La elements inhibit the generation of the REFe2 phase and tend to stay in the triple junctions, promoting the segregation of the RE/Cu/Ga elements and contributing to the formation of Ce/Nd/Cu/Ga-rich continuous thicker lamellar GBs, and as a result, weakening the detrimental effect on HA caused by La element substitution and enhancing Hcj . In addition, partial La atoms entering the RE2 Fe14 B phase are beneficial for improving the Br and temperature stability of the magnets and promoting the Ce3+ ion ratio, which also provides additional benefit for Br . The findings provide an effective and feasible way to co-enhance the remanence and coercivity of RE-Fe-B sintered magnets with high Ce content.

High cerium content (Nd-Pr-Ce)2Fe14B melt-spun ribbons with high coercivity

The effects of wheel speeds on the magnetic properties and microstructures of [(Nd,Pr)1–xCex]-Fe-B melt-spun ribbons were investigated. Compared to melt-spun ribbons with low cerium (Ce) content (x = 0.2), amorphous formation can be suppressed at high wheel speed in the ribbons with a relatively high Ce content (x = 0.8), and with the increase of the wheel speed, the magnetic properties of the ribbons with high Ce content raise continuously. At high wheel speed, the coercivity mechanism of melt-spun ribbons is mainly pinning field, and the high wheel speed introduces a large number of defects into the matrix as pinning sites. Furthermore, ribbons with high Ce content form a fine and uniform grain structure, so the grain boundary area enlarges, which further hinders the movement of domain walls. The combined effects of the above factors enable ribbons with high Ce content to have excellent magnetic properties (Hcj = 0.977 T, Mr = 64 m2 A/kg) at the wheel speed of 35 m/s.

Increased high selectivity light aromatics and furans production by co-feeding methanol to catalytic pyrolysis of cellulose with Lanthanum–Cerium bimetallic modified MCM-41 catalysts

To develop a cost-effective La-based catalyst for conversion waste biomass into high valuable chemicals, bimetallic La–Ce modified MCM-41 catalysts with different La to Ce ratios were prepared by wet impregnation method, and successfully applied to catalytic pyrolysis of cellulose with methanol as hydrogen-donor. The synergistic effect, conversion pathway for promotion of furans and aromatic and deactivation mechanism were also evaluated in co-conversion process with different technologies. Results showed that, modified MCM-41 maintained mesoporous structure, and combination La, Ce-modified MCM-41 catalysts showed the best catalytic activity due to synergistic interaction of La–O species and Ce–O species with support as well as suitable mild strong acidity. Higher La content had remarkable advantage for advancing HCs and olefin content due to higher Brønsted acid intensity, and higher Ce content was facilitated to aromatic and furans conversion due to higher mesoporous volume. 1La–3Ce/MCM-41 demonstrated the most potential for furan formation (50.18%) and 1La–1Ce/MCM-41 exhibited best deoxygenation activity and obtained more than 61.16% HCs content and 35.15% MAHs selectivity via Diels-Alder reaction assist with acid centers and metal dispersion, furthermore, 1La–1Ce/MCM-41exhibited outstanding reusability and anti-coking performance, nearly 95% yield of HCs were still maintained after regeneration. Hence, catalytic pyrolysis vapor upgrading of waste biomass with La–Ce/MCM-41 had great potential to produce valuable fuels and chemical.

Origin and implication of two newly identified peraluminous A-type granites in the early Paleozoic orogeny, Southeast Asia

Abstract: The amalgamation of the Yangtze and the Cathaysia Block in Neoproterozoic time led to the formation of the South China Block (SCB) and generated the Jiangnan Orogen with the occurrences of juvenile magmatic rocks. After this orogeny, a typical collisional orogen formed during the early Paleozoic period in Southeast Asia which is mainly distributed in the Wuyi-Nanling-Yunkai area in the SCB. However, the transitional time from syn-collisional compression to post-collisional extension is debatable. Here, we present new data on zircon U-Pb zircon ages, Lu-Hf isotopes, and geochemistry for the Guzhang and Shadi granites from the Nanling area, South China. Both plutons have similar zircon 238U/206Pb ages of ca. 430 Ma. Petrographic and geochemical characteristics (e.g., FeOt/(FeOt+MgO) = 0.82–0.95) indicate that both granites are peraluminous A-type, with high Ga/Al ratios (2.43–2.91) as well as high concentrations of Zr, Nb, Ce, Y (sum values from 327 to 527 ppm), and formation temperature (820°C–845°C). Shadi granite exhibit high positive εHf(t) values (clustering within 0 to +6) while Guzhang granite show relatively lower εHf(t) values (−8.7 to −2.9). Their mildly negative to positive zircon εHf(t) values are higher than that of many coeval granites and can be derived from anhydrous melting of tonalitic genesis in the middle crustal depth, with the Shadi pluton having more orthometamorphite in the source. The ages and Hf isotopic compositions of inherited zircons (εHf(t = 960 Ma) = 9.2, εHf(t = 950 Ma) = 7.3) suggest that the Neoproterozoic juvenile magmatic rocks in the Jiangnan Orogen were a significant source for these granites. We interpret these A-type granites derived at the post-collisional stage. Their occurrence indicates that the geological setting of this Paleozoic orogen shifted from compression to extension no later than 430 Ma.

Stepwise photoassisted decomposition of carbohydrates to H2

Stepwise photoassisted decomposition of carbohydrates to H2

Enrichment of Incompatible Elements in Alkaline Syenites in Large Igneous Provinces Due to Magma Replenishment and Reactive Porous Flow in a Mush Reservoir

AbstractUnderstanding the petrogenesis of alkaline syenites is important for constraining the mechanisms of rare earth element (REE) and rare-metal mineralization. Here we report a detailed petrological and geochemical study of early Permian syenitic rocks from the southwestern Tarim large igneous province (TLIP) in the Wajilitag area (China). We use these data to investigate the complex magmatic processes responsible for the enrichment of incompatible elements (e.g. REEs and rare metals) in these rocks. The Wajilitag syenitic rocks comprise early hornblende syenite (281 Ma) and later nepheline syenite (278 Ma), both of which are spatially and temporally associated with mafic intrusions (i.e. gabbro and diabase). These syenitic rocks show continuous variations in major elements with the mafic rocks. They also have similar Sr–Nd–Hf isotopic compositions with the nearby mafic rocks, denoting that the Wajilitag syenitic rocks should be derived from the melts represented by these mafic rocks. However, these syenitic rocks, particularly the nepheline syenites, are typically characterized by extreme enrichment of incompatible elements, which is hard to be accounted by simple fractional crystallization of mafic magmas. Some clinopyroxene phenocrysts in the Wajilitag nepheline syenites show oscillatory zoning with strikingly increasing and then gradually decreasing MgO contents, which recorded replenishment of mafic magma at the interval. Low-MgO clinopyroxene mantles and/or rims have much higher incompatible element contents (e.g. Nb, Ce, and Zr) and ratios (e.g. Ce/Y) than their cores, which could reflect melt injection controlled by reactive porous flow in a mush reservoir of a crustal magma chamber. Such processes may also cause the high Ce and/or Nb contents of the mantles and/or rims of zoned titanite and apatite phenocrysts. The injection of reactive porous flow melts is the key process that produces the extreme enrichment of incompatible elements in the alkaline syenites from the western TLIP, as well as other plume-related alkaline syenites that host world-class REE and rare-metal deposits.

Biogeochemical cycling of Cd, Mn, and Ce in the Eastern Tropical North Pacific oxygen‐deficient zone

AbstractOxygen‐deficient zones (ODZs) play an important role in the distribution and cycling of trace metals in the ocean, as important sources of metals including Fe and Mn, and also as possible sinks of chalcophile elements such as Cd. The Eastern Tropical North Pacific (ETNP) ODZ is one of the three largest ODZs worldwide. Here, we present results from two sectional surveys through the ETNP ODZ conducted in 2018, providing high‐resolution concentrations of several metals, along with complimentary measurements of nutrients and iodine speciation. We show that samples obtained from the ship's regular rosette are clean for Cd, Mn, Ni, and light rare earth elements, while uncontaminated Fe, Zn, Cu, and Pb samples cannot be obtained without a special trace‐metal clean sampling system. Our results did not show evidence of Cd sulfide precipitation, even within the most oxygen‐depleted water mass. High Mn and Ce concentrations and high Ce anomalies were observed in low‐oxygen seawater. These maxima were most pronounced in the upper water column below the oxycline, coincident with the secondary nitrite maxima and the lowest oxygen concentrations, in what is generally considered the most microbially active part of the water column. High Mn and Ce features were also coincident with maxima in excess iodine, a tracer of shelf sediment sources. Mn and Ce maxima were most prominent within the 13°C water mass, spanning a density horizon that enhances isopycnal transport from the shelf sediments, resulting in transport of Mn and Ce at least 2500 km offshore.

Highly stable Mo-based bimetallic catalysts for selective deoxygenation of oleic acid to fuel-like hydrocarbons

To develop efficient, economical and environmentally friendly Mo-based bimetallic Al/MCM-41 catalysts for catalytic oleic acid pyrolysis into hydrocarbon-like upgrading biofuel, a series of metal-modified Mo-based catalysts was successfully synthesized. The effects of different metal oxide types (Zr, Zn, Pt, Cu, Co, Ce, Ni) and Ce to Mo mixed ratios were compared and characterized by XRD, BET, NH3-TPD, XPS, SEM and TEM technologies. Simultaneously, the deoxygenation effect and reusability properties were also evaluated by Py-GC/MS and TGA. The results showed that the molybdenum-based bimetallic catalyst exhibited superior deoxygenation activity (Ce>Cu>Zn>Ni>Zr∼Pt>Co) in the decarbonylation and decarboxylation pathways. Higher deoxygenation activity was related to rich surface Ce-□-Mo synergistic oxygen vacancies, suitable metal-Lewis and Brønsted acidity and excellent textural properties. A higher Ce content was beneficial to HC and aromatic formation due to a higher specific surface area and mesoporous volume, and a higher Mo content facilitated olefin and alkane conversion due to a higher Brønsted acid intensity and smaller pore size. The 3Ce-1Mo/Al-MCM-41 exhibited excellent catalytic activity and promising reusability by yielding 97.72% hydrocarbons, 75.33% aromatic content and 57.92% MAHs due to the synergistic effect between Ce and MoOx, rich surface Ce-□-Mo synergistic oxygen vacancies and suitable metal-Lewis and Brønsted acid intensities that contributed to better reaction activity and coke resistance and activated the CO of oleic acid. The slight reduction in HCs was mainly due to the loss of active metal sites and coke deposition. Furthermore, the synergistic effect of Ce and MoOx species obviously advanced the reaction activity and coke resistance.

Diverse early diagenetic processes of ferromanganese nodules from the eastern Pacific Ocean: evidence from mineralogy and in-situ geochemistry

ABSTRACT Ferromanganese nodules are a potential energy resource because of their high contents of economically interesting elements (i.e. Mn, Ni, Cu, and Zn). These are higher in diagenetic layers than in hydrogenetic layers. The study of the causes of elemental accumulation in the diagenetic layer is useful for the exploration metal-rich nodules. A diagenetic-dominant ferromanganese nodule, from the central Clarion–Clipperton Fracture Zone of the eastern Pacific Ocean was studied from core to rim. It was divided into four layers and seven sublayers, of the four typical diagenetic sublayers (L1, L2-1, L2-2, and L3-1). Differences were observed in these diagenetic sublayers. L1 presents the highest Mn/Fe ratio (54), the lowest Co content (2262 ppm), and a positive Ce anomaly. L2-1 exhibits high Co (3122 ppm) and Ba contents (4020 ppm), a positive Ce anomaly, and an obvious peak for 10 Å manganate minerals. L2-2 contains the lowest Ni+Cu contents (3.2 wt%), the highest Ba and Co contents (5110 ppm), and the strongest positive Ce anomaly. In L2-2, the δCe value can be positively correlated to the Mn/Fe ratio and a pronounced peak for 10 Å manganate minerals indicates that this layer has the highest mineral crystallinity. L3-1 shows the highest Ni+Cu contents (5.4 wt%), the lowest Ba (1247ppm), and Co (1725 ppm), a weakly positive Ce anomaly, and the poorest mineral crystallization. Diagenetic- and hydrogenetic-endmember mixing models reveal that hydrogenetic input contributes minimally to these chemical changes, whereas diagenetic input contributes greatly. The changes in diagenetic input may be caused by the changes in primary productivity brought about by movement of tectonic plates and the intense activity of the diagenetic pore fluid. The activity may provide a metal source for the diagenetic sublayer (anomalously high Co and Ce content) via the incorporation of metals released from dissolved buried nodules and micronodules under a suboxic or reducing environments.

Effect of metal-doping (Me = Fe, Ce, Sn) on phase composition, structural peculiarities, and CO oxidation catalytic activity of cryptomelane-type MnO2

Manganese oxides attract considerable attention as redox catalysts for abatement of environmental pollutants due to their relatively high activity and low costs contrary to noble metal catalysts. The present work is focused on the effect of cryptomelane-type MnO 2 catalyst modification with Fe 3+ , Ce 3+ /Ce 4+ , Sn 4+ on their phase composition, structural peculiarities, and catalytic activity in CO oxidation. The samples are investigated by XRD, Raman spectroscopy, XPS, XRF, and comprehensive HRTEM, with their catalytic activity being studied under the model dry conditions and simulated real exhaust conditions comprising CO, O 2 , and water balanced by inert. The Mn 4+ substitution in the cryptomelane structure by Me n+ is revealed to result in its monoclinic distortion, with the Sn- and Fe-doped cryptomelane-type MnO 2 formation being accompanied by the formation of SnO 2 and Fe 1−x Mn x O 3 /Fe 1+x Mn 2−x O 4 , respectively. For Ce-doped samples, the K + presence in the cryptomelane tunnels is essential to stabilize the cryptomelane structure and nanorod morphology. The cryptomelane structure stabilized by only Ce n+ cations is collapsed during the sample calcination to form Mn 2−x Ce x O 3 and Mn 3−x Ce x O 4 , while high Ce content does not favor the formation of the cryptomelane-type MnO 2 . The composites based on the Me-doped cryptomelane-type α-MnO 2 , especially those doped with Ce, are shown to be promising candidates to develop effective oxide-based catalysts for CO oxidation. • Mn 4+ substitution by Me n+ results in monoclinic distortion of cryptomelane structure. • K + ions are essential to stabilize cryptomelane structure and nanorod morphology. • Doped cryptomelane-type MnO 2 is promising for designing of new CO oxidation catalysts.

Combining molybdenum carbide with ceria overlayers to boost Mo/CeO2 catalyzed ammonia synthesis

AbstractThe design of an efficient non‐noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low‐valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo‐based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis.

Morphological Mapping of Hydrothermally Synthesised Nanoceria at High Ce Concentrations

AbstractSynthesis methods for different nanoparticulate morphologies are of increasing importance since the morphological features determine the redox performance in many applications. However, the effects of synthesis variables on the formation of these morphologies are not well understood and previous work has been limited to relatively low [Ce] and [NaOH]. The present work reports an investigation of the morphological development of nanoceria through the examination of the key processing variables for precipitation and hydrothermal synthesis at high [Ce] and [NaOH]. Characterisation included XRD, Raman, TEM, HRTEM, SAED, XPS, and BET. The resultant refined morphological map delineates the effects of [NaOH] and temperature on the morphological evolution of ceria nanoparticles synthesised from Ce(NO3)3 aqueous solutions in terms of morphology and grain size. The data show that temperature dominates the morphology but elevated [NaOH] and temperature both increase the nanoparticle size. Compared to synthesis at low concentrations, high [Ce] also promotes grain growth, although this is secondary to the effect of [NaOH]. Significantly, the increased grain sizes also enhance the concentrations of catalytically active sites (Ce3+ and charge‐compensating oxygen vacancies). The present work provides a platform of fundamental concepts for the control of experimental variables to synthesise predictable nanoparticulate characteristics.

Radiation-Resistant Er-Doped Fiber Based on Ge-Ce Co-Doping

We investigated the radiation responses of Ge-Ce co-doped erbium-doped fibers (EDFs) under gamma radiation with a dose up to 1000 Gy and a dose rate of 0.2 Gy/s. Three EDFs with low or high concentrations of Ge or Ce were fabricated by modified chemical vapor deposition (MCVD). The absorption spectra and amplification performance of the three Ge-Ce co-doped EDFs before and after radiation were tested and analyzed in detail. The radiation-induced absorption (RIA) can be dramatically weakened by heavily co-doping Ge and Ce, and 0.8 dB radiation-induced gain degradation at 1550 nm was obtained in the erbium-doped fiber amplifier (EDFA) with heavy Ge and Ce doping at a dose of 1000 Gy. Furthermore, the possible mechanism of Ce and Ge effects on radiation tolerance enhancement is discussed. Relevant results indicate that the Ge-Ce co-doped EDF has significant performance improvements in radiation resistance, making it ideal for applications in harsh radiation environments.

Cerium-terephthalic acid metal-organic frameworks for ratiometric fluorescence detecting and scavenging·OH from fuel combustion gas

Hydroxyl radical (•OH) in fuel combustion gas seriously damages human health. The techniques for simultaneously detecting and scavenging •OH in these gases are limited by poor thermal resistance. To meet this challenge, herein, metal organic frameworks (MOFs) with high thermal stability (80–400 °C) and dual function (•OH detection and elimination) are developed by coordinating Ce ions with terephthalic acid (TA) (Ce-BDC). Due to the reversible conversion between Ce3+ and Ce4+, and the high concentration of Ce3+ on the surface of Ce-BDC MOFs (89.6%), an •OH scavenging efficiency over 90% is realized. Ratiometric fluorescence (I440 nm/I355 nm) detection of •OH with a low detection limit of ∼4 μM is established by adopting Ce ions as an internal standard and TA as an •OH-responsive fluorophore. For real applications, the Ce-BDC MOFs demonstrate excellent •OH detection sensitivity and high •OH scavenging efficiency in gas produced from cigarettes, wood fiber and machine oil. Mouse model results show that the damage caused by •OH in cigarette smoke can be greatly reduced by Ce-BDC MOFs. This work provides a promising strategy for sensitively detecting and efficiently eliminating •OH in fuel combustion gas.

Cerium Oxide Nanoparticles with Entrapped Gadolinium for High T 1 Relaxivity and ROS-Scavenging Purposes.

Gadolinium chelates are employed worldwide today as clinical contrast agents for magnetic resonance imaging. Until now, the commonly used linear contrast agents based on the rare-earth element gadolinium have been considered safe and well-tolerated. Recently, concerns regarding this type of contrast agent have been reported, which is why there is an urgent need to develop the next generation of stable contrast agents with enhanced spin–lattice relaxation, as measured by improved T1 relaxivity at lower doses. Here, we show that by the integration of gadolinium ions in cerium oxide nanoparticles, a stable crystalline 5 nm sized nanoparticulate system with a homogeneous gadolinium ion distribution is obtained. These cerium oxide nanoparticles with entrapped gadolinium deliver strong T1 relaxivity per gadolinium ion (T1 relaxivity, r1 = 12.0 mM–1 s–1) with the potential to act as scavengers of reactive oxygen species (ROS). The presence of Ce3+ sites and oxygen vacancies at the surface plays a critical role in providing the antioxidant properties. The characterization of radial distribution of Ce3+ and Ce4+ oxidation states indicated a higher concentration of Ce3+ at the nanoparticle surfaces. Additionally, we investigated the ROS-scavenging capabilities of pure gadolinium-containing cerium oxide nanoparticles by bioluminescent imaging in vivo, where inhibitory effects on ROS activity are shown.

Magnetic properties and coercivity mechanism of high Ce-content CeNdFeB film with Tb diffusion

Magnetic properties and coercivity mechanism of an anisotropic Ce–Nd–Fe–B film with a high Ce content (70 at. % Nd is replaced by Ce) have been investigated. After grain boundary diffusion with Tb layers, an enhancement of coercivity from 4150 to 9250 Oe is observed. Combining the initial magnetization curves, micromagnetic theory, and in-siut observation of magnetic domains in the demagnetization process, it is confirmed that the coercivity mechanism for the high-Ce-content magnets is the mixed type dominated by the pinning mechanism. Moreover, as the thickness of the Tb diffusion layer increases, the pinning center of domain walls changes from narrow planar inhomogeneities to wide planar inhomogeneities. A growing role of pinning plays in determining the coercivity of samples with increasing the thickness of Tb layer due to the increase in magnetocrystalline anisotropy after Tb substitution in the RE2Fe14B phase. In addition, the CeFe2 intergranular phase leads to the enhancement of coercivity due to decoupling the hard magnetic phase grains. Our results provide an insight into the coercivity mechanism of high-Ce-concentration Ce–Nd–Fe–B magnetic materials and promote the comprehension of the effect of Tb diffusion in the magnetization reversal process.